Generation of carbon monoxide and hydrogen by underground gasification of coal



E. F- PEVERE ET AL GENERATION OF CARBON MONOXIDE AND HYDROGEN 4 April16, 1957 2,788,956

BY UNDERGROUND GASIF'ICATION OF COAL I Filed Aug. 3, 1955 med SmePuefOGENERATION 01 MONOXIDE' HYDROGEN BY UNDERGROUND GASIFICA- TION F COAL Ia Ernest'F. Pevere, Reac ing-mu Hom ny. Hess, Glenliam, N". Y.,assignurs-to The. Texas Company; New York, N. Y., a corporation. ofDelaware Application August 3, 1955, Serial No. 526,163 fiGlaiins".'(Cl.-262-"-$) This application relates-tothe partial combustionof coalinunderground seams. in one of itsmore specific aspects, the inventionrelates to a method for preparing coal beds for'undergroundgasification. 7

Since 1933', the underground gasification-of coal has been seriouslyinvestigated and exploited by a special Russian trust, Podzem, andextensive Russian literature has grown out of this work. Areviewin-English by Chel-tin was published in Collary Garden 162, 1193-6(1936) and Fuel Economist ll, 331- (l 936). Since. the end of World WarII, this problem has been seriously examined in England, France, Belgiumand the UnitedSta'tes. A review by M. L. Kastems'appeared in Chemicaland Engineering News, March 24,. 1952.

Underground gasification of coal hasbeen carried out in a number ofcases with encouraging results. In preparing the coal seamforgasification, it is generally necessary to drive two parallel maindrifts through .the:coal seam, one as an inlet andthe other as anoutlet, and to connect these shafts with one or more-lateral drifts atright angles to the main drifts. A combustion-supporting gas, e. g. air,oxygen or'other gas' con'taining'free oxygen is introduced through oneof the main drifts and products of combustion are withdrawn through theother. Steam or carbon dioxide may be used in conjunction with air,oxygen, or a mixture of air and oxygen as the gasifying medium orcombustion-supporting gas. Combustion is initiated by igniting the.co'al along the path of flow, usually at the lateral cross drifts. Themain drifts may be used alternately as inlets and outlets. Afterthe coalseam is fired, air or oxygen is blown through the corridorto bring thesurface of the coal tofthe desired temperature, and then steam is blownin either alone or withair or oxygen. If steam alone is used, the flowof steam must be periodically interrupted and the coal seam'firedwithcombustionsupporting gas to maintain .the required temperature. Amixture of steam with oxygen or air may be used for continuousgasification. Thegas produced generallyhas a low B. t. u. value, aresult which is not unexpected due to poor contact of the coal with thesteam and oxygen.

It has been proposed previously to prepare a portion of a coal seam forgasification by breaking the coal loose from the bed by mining methodsand then passing the reacting gases through the lumps ofcoal. Althoughthis procedure results in effective contact between thecoai and thegasesit obviously is a costly one. By the process of this invention the coalseam is prepared for underground g'asifica'tion insuch-a way thatintimate contact between the coal and the gaseous reactants isobtainedwithout the necessity of mining the coal from the seam.

In accordance with this inventiona mineral acid having solvent power forone or more' of the constituents of the coal is brought into contactwith theicoal seameffecting solution of coal substance; Preferably,theacidi. is permitted to drip onto the coal at a pluarlity of points.The acid forms a multitude of passages through the coal which areirregular in shape and which are very permeable to gaseous reactantsused for the gasification of coal.

In a specific embodiment of. the presentinvention a main channel orpassageway is drilled throughan upper portion of the coal seam,preferably as near as possible to the top-of the seam, while asecond-"main passageway Patented Apr. 16; 1957 stantially parallel tothe upper passageway. In general, the passageways are parallel to thebedding; plane of the coal seam. Theprocess of the invention remains thesamefor an inclined seam as for a horizontal seam. The acid isintroduced through the upper main passageway or drift. The acidpercolates downward through. the coal seam and eventually reaches thelower main passageway. Intermediate .passagewaysparallel to the mainpassageways may be :provided and are particularly-advantageous in thickbeds.

In .a preferred embodiment of. the present invention strong sulfuricacid containing percent sulfuric acid by weight is introduced slowlyintocontact with the coal in the=upper partof. the. seam- Strong sulfuricacid may be introduced through the passageway-into contact with thecoalseam through a steel .tube. The tube may be perforated to distributethe acid along the desired section of the passageway. With other acidsother types of acid resistant tubing. are required, e. g. plastic orsynthetic rubber tubes.

St-rongmineral acids, e. g. hydrochloric, hydrofluoric, nitric, andsulfuric acids, are useful in the processof this invention. The acidconcentration should exceed 30 weight percent. Higher concentrations ofsulfuric and nitric acids are desirable. Sulfuric acid in. excess. of 90weight percent is preferred.

Selective gasification of'the coal seam may be accomplished'by treating.sections of the seam with acidv and leaving pillar-s or untreatedsections of the coal seam between treated sections. One or more of thetreated sections may be ignited while others are blocked off.

Preferably the-reaction is initiated in an upper passageway, thegasification proceeding downwardly through the c'oal b'ed to a lowerpassageway. As indicated above, exit passageways may be provided atvarying depths and are particularly useful inthick seams of coal.

Firing of the coal may be initiatedin any of a number of ways,fo'rexample by pumping a colloidal or semicolloidal dispersion ofphosphorus in water, or phosphorus in carbon disulfide into the upperpart of the pretreated section of the coal. As the carrier liquidtrickles downwardly through the treated section, phosphorus is depositedon .thelco'al. Afterthe bed has been pretreated with the phosphorussolution, an oxygen-containing gas is'introduced which, upon contactwith the phosphorus, ignites simultaneously and thereby ignites thecoal. Once the reaction commences it isself sustaining so long as anadeguate supply of oxygen-containing gas is provided.

The" figure is a diagrammatic sectional view through a section of theearth illustrating the application of the process of this invention tounderground gasification of coal.

With reference to the figure, a well 1 is drilled into or through thecoalseam. A main passageway 2 is then drilled along the upper part ofthe coal seam. Means for horizontal drilling and directionaldrilling-are known in the art. Generally, a deflecting device known as awhipstock is positioned in the well 'at the desired depth and a rotatingdrill bit on a flexible conduit is operated fromth'e whipstock' toeffect horizontal 'or near-horizontal drilling. After a horizontal boreZof the desired length. has been drilled, the bit is removed, thewhipstock is lowered and a second bore 3 is drilled through the coalseam parallel to and below bore 2. Bore 3 forms the second mainpassageway. Obviously a number of such passageways may be drilledthrough the coat seam. The portion of well 1 below bore 2 is then filledwith cement 4. A second well 6 is drilled into the coal seam tointersect passageway 3-. Well 6 may be enlargedat its lower end'b'ymeans of explosive charges.

A conduit 7, closed at its end andprovid'e'd witha series ofperforations8; is; theniutr'oduced into the-upper main passageway 2. Strong mineralacid, e. g. sulfuric acid, is

pumped through conduit 7 from which it escapes through perforations 8into section AA' of the coal seam. The 7 necting the upper mainpassageway 2 with the lower main passageway 3. Similarly, other sectionsof the coal seam, e. g. section BB' may be acid treated. Following acidtreatment, an ignition agent may be introduced through pipe 7. Followingpreparation pipe 7 is withdrawn from the well bore. A combustionsupporting gas is then introduced through one of the wells, preferablythrough well 1 into the upper horizontal pasageway 2. The coal seam is,ignited at the top of the treated section. The oxygen-containing gasstream passes down through channels formed by the acid in the treatedsection. As the coal is consumed, combustible gas comprising carbonmonoxide and hydrogen is generated. The combustible gas, together withvolatile constituents distilled from the coal, is collected in the lowerpasageway 3 and produced through well 6 to the surface.

The coal seam may be ignited initially in any suitable manner, as byelectrical means or by a squib or incendiary shell, placed in contactwith the coal in the horizontal passageway 2.

Air or relatively pure oxygen may be employed as the source ofoxygen-containing gas. Relatively pure oxygen is preferred from thestandpoint of producing gas which contains a minimum amount of nitrogenand other inert constituents. Once combustion is well established, steammay be introduced either continuously, in admixture with oxygen oroxygen-containing gas, or intermittently as in gas making apparatus withalternate blast and blow gas make cycles. Steam helps to control thetemperature in the formation and produces hydrogen.

It will be understood that although passageway 2 is preferred as theinput passageway for the combustionsupporting gas, either mainpassageway 2 or 3 may be used as the input pasageway while the other isused as the outlet passageway. It will also be understood that either ofthe main passageways may be drilled through well 6.

i In an alternative procedure, channels between passageways 2 and 3 arefirst made by hydraulic fracturing of'the coal seam between thepassageways. In this case, hydraulic fluid under pressure, suitablywater or oil with or without thickeners or viscosity increasingadditives, is introduced through well 6 into passageway 3 undersufficient pressure to fracture the coal seam and form cracks extendingupwardly toward or even as far as passageway 2. Similarly, hydraulicfluid under pressure may be introduced through well 1 into the upperpassageway 2,

fracturingthe coalseam between bores 2 and 3. The

liquid is withdrawn, the grains of sand or gravel serve to help preventthecracks from closing. Following hydraulic fracturing, acid isintroduced through passageway 2 onto the top of the coal seam. The acidper- .colates down through the fissures, forming auxiliarypassageways'interconnecting the main passageways. The gasifying mediummay be readily passed through the auxiliary passageways.

Spent acid may be withdrawn from the coal seam through passageway 3 andwell 6. Ordinarily it is not necessary to separately withdraw the spentacid. Acid recovery is efiected by processing the product gas. Freshacid thus may be made up for additional treatment opcrations. Sulfuricacid is a preferred acid because of the natural occurrence of sulfurincoal. Obviously, many modifications and variations of the invention, asherein'before set forth, may be made without departing from the spiritand scope thereof and therefore only such limitations should:be made asare'indicated in the appended claims.

Weclaimz. 1. In a process forthe underground gasification of coal inwhich an exothermically-reacting gas is introduced into contact with thecoal in situ, the coal is reacted with said gas, and gaseous products ofreaction are withdrawn from the coal bed, the improvement whichcomprises forming a first main passageway through an upper portion ofthe 'coal bed along the seam, forming a second main passageway through alower portion of the coal bed along the seamsubstantially parallel toand below said first passageway, fonning aum'liary passagewaysinterconnecting said main passageways by introduction of strong mineralacid through said first passageway into contact with said coal eifectingsolution of coal substance in said acid, and

thereafter supplying reactant gas to one of said main passageways, andwithdrawing gaseous products from the other of said main passageways.

2. A process as defined in claim 1 wherein said acid is sulfuric acid.

3. A process as defined in claim 1 wherein said acid is nitric acid.

4. A process as defined in claim 1 wherein said acid is hydrochloricacid.

5. In a process for the underground gasification'of coal wherein acombustion-supporting gas is introduced into contact with the coal insitu, the coal is ignited, and gaseous products of reaction arewithdrawn from the coal bed, the improvement which comprises forming afirst main passageway through an upper portion of the coal bed along theseam, forming a second main passageway through a lower portion of thecoal bed along the seam substantially parallel to and below said firstpassageway, and introducing strong mineral acid through said first mainpassageway into contact with the bed of coal at a plurality ofselectedpoints along said first main passageway thereby effectingsolution .of coal substance and forming auxiliary vpasagewaysinterconnecting said main passageways,

. 6. In a'pro'cess for .the underground gasification of coal wherein acombustion-supporting gas isintroduced into contact with the coal insitu, the coal is ignited, and gaseous products of reaction arewithdrawn from the coal bed, the improvement which comprises forming afirst main passageway through an upper portion of the coal bed .alongthe seam, forming a second main passageway through a lower portion ofthe coal bed along the seam substantially parallel to and below saidfirst passageway, introducing liquid under pressure through at least oneof said mainpassageways eflecting fracturing of said coal seam andforming fluid permeable channels interconnecting said main passageways,withdrawing said fracturing liquid and introducing a strong mineral acidinto said first main passageway and through said channels into saidsecondmain passageway effecting solution of coal substance in saidstrong mineral acid, withdrawing reaction products of said acid fromsaid coal bed, introducing combustion-supporting fluid through one ofsaid main passageways, and withdrawing gaseous products of reaction fromthe other of said main passageways.

References Cited in the file of this patent UNITED STATES PATENTS2,630,306 I Evans Mar. 3', 1953

1. IN A PROCESS FOR THE UBDERGROUND GASIFICATION OF COAL IN WHICH ANEXOTHERMICALLY-REACTING GAS ID INTRODUCED INTO CONTACT WITH THE COAL INSITU, THE COAL IS REACTED WITH SAID GAS, AND GASEOUS PRODUCTS OFREACTION ARE WITHDRAWN FROM THE COAL BED, THE IMPROVEMENT WHICHCOMPRISES FORMING A FIRST MAIN PASSAGEWAY THROUGH AN UPPER PORTION OFTHE COAL BED ALONG THE SEAM, FORMING A SECOND MAIN PASSAGEWAY THROUGH ALOWER PORTION OF THE COAL BED ALONG THE SEAM SUBSTANTIALLY PARALLEL TOAND BELOW SAID FIRST PASSAGEWAY, FORMING AUXILIARY PASSAGEWAYSINTERCONNECTING SAID MAIN PASSAGEWAYS BY INTRODUCTION OF STRONG MINERALACID, AND THROUGH SAID FIRST PASSAGEWAYS INTO CONTACT WITH SAID COALEFFECTING SOLUTION OF COAL SUBSTANCE IN SAID ACID, AND THEREAFTERSUPPLYING REACTANT GAS TO ONE OF SAID MAIN PASSAGEWAYS, AND WITHDRAWINGGASEOUS PRODUCTS FROM THE OTHER OF SAID MAIN PASSAGEWAYS.